Determination of an exact location of a mobile receiver in an urban environment can be quite challenging, especially when the receiver is located in a multi-story building. Imprecise estimates of the receiver's altitude, for example, can delay emergency response, forcing emergency response units to search several floors instead of one floor. Identifying the wrong floor level could also disrupt efforts to restrict, grant, or track a user's access to rooms or information based on the location of that user. Similarly, inaccurate estimates of position may frustrate the user by extending navigation times.
One aide in determining a receiver's altitude with acceptable accuracy uses atmospheric reference data (e.g. atmospheric pressure and temperature) measured at different atmospheric reference nodes having atmospheric sensors of known altitudes in a region within which the receiver resides. Such reference nodes may provide the atmospheric reference data with various levels of accuracy depending on the implementation (e.g. measured pressure within 10 Pascals of true pressure at least 90% of the time, and measured temperature within a few degrees of true temperature 90% of the time).
Unfortunately, atmospheric reference data from a particular reference node can be unreliable at times because of various issues. Localized weather phenomena may affect the reliability of the atmospheric reference data—e.g. wind, humidity, or fluctuations in air temperature can affect pressure measurements. The reliability of atmospheric reference data may also be affected by other adverse conditions like overheating of the reference node due to sun effects, sensor drift of the reference node, poor calibration of the reference node, and other conditions. Thus, it may be advantageous to selectively not use unreliable atmospheric reference data from certain reference nodes.
Clearly, systems and methods for identifying reliable or unreliable atmospheric reference data are needed.